Surgical Training for the Implantation of Neocortical Microelectrode Arrays Using a Formaldehyde-fixed Human Cadaver Model

Summary

We designed a procedure in which a formaldehyde-fixed human cadaver is used to assist neurosurgeons in training for the implantation of microelectrode arrays into the neocortex of the human brain.

Abstract

This protocol describes a procedure to assist surgeons in training for the implantation of microelectrode arrays into the neocortex of the human brain. Recent technological progress has enabled the fabrication of microelectrode arrays that allow recording the activity of multiple individual neurons in the neocortex of the human brain. These arrays have the potential to bring unique insight onto the neuronal correlates of cerebral function in health and disease. Furthermore, the identification and decoding of volitional neuronal activity opens the possibility to establish brain-computer interfaces, and thus might help restore lost neurological functions. The implantation of neocortical microelectrode arrays is an invasive procedure requiring a supra-centimetric craniotomy and the exposure of the cortical surface; thus, the procedure must be performed by an adequately trained neurosurgeon. In order to provide an opportunity for surgical training, we designed a procedure based on a human cadaver model. The use of a formaldehyde-fixed human cadaver bypasses the practical, ethical and financial difficulties of surgical practice on animals (especially non-human primates) while preserving the macroscopic structure of the head, skull, meninges and cerebral surface and allowing realistic, operating room-like positioning and instrumentation. Furthermore, the use of a human cadaver is closer to clinical daily practice than any non-human model. The major drawbacks of the cadaveric simulation are the absence of cerebral pulsation and of blood and cerebrospinal fluid circulation. We suggest that a formaldehyde-fixed human cadaver model is an adequate, practical and cost-effective approach to ensure proper surgical training before implanting microelectrode arrays in the living human neocortex.

Introduction

Recent years have seen the development of technological solutions to the challenge of recording the activity of multiple individual neurons in the living brain^1,2,3. Silicon-based microelectrode arrays perform similarly to conventional wire microelectrodes in terms of signal properties, and they can record from dozens to hundreds of neurons in a small patch of cerebral tissue^4,5,6,7. Microelectrode arrays have allowed scientists to establish the cor

Protocol

The human cadaver used in this work was provided under the framework of body donations for medical education. Informed consent for body donation was obtained in writing during the lifetime of the donor. In accordance with the federal and cantonal laws, no review by an ethics committee was necessary.

Note: This protocol assumes that the persons performing the practice surgery are neurosurgeons with training and expertise in standard neurosurgical procedures, including patient positioning and head fixation, craniotomy and durotomy, and suturing. In addition to the tools and equipment specific to the microelectrode array, standard neurosurgica

Results

Our protocol uses a formaldehyde-fixated human cadaver model to allow surgeons to practice the surgical procedure of implanting a microelectrode array into the cerebral neocortex in a realistic, OR-like environment. The option of performing post-mortem neuroimaging, such as head CT, will confirm the absence of any significant intracranial lesion (Figure 1A) and can help with the selection of the implantation site. Working with an entire specimen and setting up for surgery on an operating tab...

Discussion

The formaldehyde-fixed human cadaver model and the surgical protocol described here replicate the surgical procedure of implanting microelectrode arrays into the human cerebral neocortex. Each step of the procedure, including the positioning of the microelectrode array and its insertion with the pneumatic inserter, proceed in almost the same fashion as in a real-life patient, with the exception that cerebral pulsation and circulation are absent. The critical steps in the protocol are the alignment of the microelectrode a...

Materials

Name	Company	Catalog Number	Comments
Mayfield skull clamp	Integra LifeSciences, Cincinnati, OH	A1059
Midas Rex MR7 system for craniotomy	Medtronic, Minneapolis, MN	EC300
Dura scissors	Sklar Surgical Instruments, West Chester, PA	22-2742
Self-tapping bone screws	OrthoMed Inc., Tigard, OR	OM SYN211806
Microelectrode array and pedestal	Blackrock Microsystems, Salt Lake City, UT	LB-0612	Mock-up arrays are available from the manufacturer upon request
Pneumatic impacter	Blackrock Microsystems, Salt Lake City, UT	LB-0088
64-channel electrocorticography grid	Ad-Tech Medical Instrument Corporation, Racine, WI	FG64C-SP10X-0C6	Optional